Which material sounds better for speakers construction? Wood, Ply or MDF?

Feed the speaker the impulse and rejoice or weep with the results.....
the cabinet stores and releases energy
how much, at what frequency and over what amount of time is critical
people do like all manner of distortion, coloration, etc....
the fact of the matter is there are few if any cost no object designs out there, so MDF in hands of capable designer is a very cost effective material.....

i should probably disclose i use a bunch of Vandersteen and HRS products......

i checked w RV
he invented the trade secret constrained layer damping material used in Treo up thru model 7 and it’s initial use predates HRS.

motion into heat
simple to say
not so easy to do at the correct range of frequencies.....

RV is a measurement and science based engineer, I can assure you that the 7 cabinet is superior to the 5a in every way.
impossible to overdamp a passive component like a cabinet - you want to hear the Stradivarius or the cabinet ?
the 7 cabinet is a mdf  cabinet within a mdf cabinet with constrained layer damping ( he collaborate s with Michael at HRS, so my guess is that is is HRS supplied ( and you just know they are serious engineers ) and CF wrap cooked in an Autoclave.
in a previous working life I dabbled in advanced composite structures... running arguably some of the most advanced high technology composite shops on the planet- simple stuff like the Hubble optical bench, F-22 wings, 787 fuselage.....
easy stuff...
i can assure you it is more than veneer
now from a musical perspective, while I loved my 5a for many many musical years, the 7 mk 2 are lightyears on....

enjoy....

cueing up some late nite Sunday massed chorale..... perfect for a prayer of discernment....